Bios, cmos and post

BIOS, CMOS and POST
motherboard Chip
Hardware For A+

1. BIOS, CMOS and POST

2. BIOS BIOS is short for Basic Input/output System This small program is used to startup the computer communicate with hardware before an operating system is loaded BIOS is stored in ROM chips on the mainboard Some chips contain programs to support basic hardware such as parallel and serial ports, keyboard and the speaker

3. Stores the CMOS (complementary metal-oxide semiconductor) chip stores information that is subject to change settings such as time/date, power saving settings, and video adapter, hard drives and other device settings CMOS settings can be changed in the CMOS Setup BIOS settings are applied at every startup

4. CMOS Settings can mostly be entered by pressing the DEL or F2 key during startup (depends on manufacturer, other key or key combinations might apply) Most main boards have a "CMOS restore to factory defaults“ jumper which allows you to return to the default CMOS settings configured by the manufacturer. This is useful when you cannot access the CMOS Setup because of incorrect CMOS settings or lost CMOS passwords. Make sure the power is completely off when you shorten the jumper.

5. CMOS Battery The information contained in the CMOS chip is maintained by a battery If the battery runs low, the CMOS content will be lost and POST will display a "CMOS invalid" or "CMOS checksum invalid" message

6. BIOS Upgrades Upgrading the BIOS is called flashing Most modern BIOSs are stored on flash memory, this enables you to upgrade the BIOS software when needed, in some cases this is necessary to support new hardware technologies/devices Some main boards allow replacing the BIOS ROM, although this is not done often

7. POST During startup the BIOS also invokes The POST (Power On Self Test) program that runs multiple self-diagnostic routines When the computer does not pass the POST it will display an error code or message, or generate a beep code through the speaker when display is not functioning Failing the POST does not always mean the computer will not be able to boot required devices that need to pass the POST are CPU, RAM, display adapter and boot device

8. but if the floppy drive is missing the computer can still be able to continue the boot process The meaning of the beep codes vary depending of the manufacturer Although most BIOS manufacturers started using error text messages , some use numeric POST error codes . Some of them are listed below:

9. POST error code Probable Cause 1xx Mainboard related errors 200-299 Memory related errors. 3xx Keyboard related errors 151 Real-time clock failure 161 BAD CMOS memory 6xx Floppy Disk related errors 1700-x Hard drive controller 31xx Network Adapter related errors

10. COMMON CMOS SETTINGS Floppy drive s Hard drives Boot sequence This setting is used to determine in which order devices (e.g. CD, floppy or hard disks) the computer should look for a boot sector. Date/Time The Date and Time is set in the BIOS, stored in CMOS, maintained by CMOS battery.

11. Passwords In most cases a user (startup) password and a supervisor (setup) password can be set in the CMOS. When a Setup password is required the computer will prompt for it when you try to access the BIOS setup. When a Startup password is configured the computer will prompt for it at every startup. The CMOS password can be reset by shortening the "CMOS restore to factory defaults jumper" or by temporarily removing the CMOS battery.